MEMS devices, such as MEMS mirrors, are effective in a variety of optical applications, including high-speed scanning and optical switching. FIG. 1 shows a prior art optical system, which employs an array of MEMS mirrors to couple light from input fibers to output fibers. Particularly, FIG. 1 depicts a wavelength-separating-routing (WSR) apparatus 100 including an array of fiber collimators 110, which provide one or more input and output ports (e.g., ports 110-1 through 110-N); a wavelength-separator, which in one form may be a diffraction grating 101; a beam-focuser in the form of a focusing lens 102; and a MEMS device 103, which may be an array of micromirrors.
In operation, a multi-wavelength optical signal emerges from one or more input ports, e.g., port 110-1. The diffraction grating 101 angularly separates the multi-wavelength optical signal into multiple spectral channels. Each spectral channel may represent a distinct center wavelength (e.g., λi) and associated bandwidth, and may carry a unique information signal as in WDM optical networking applications. The focusing lens 102 focuses the spectral channels into a spatial array of corresponding focused spots (not shown in FIG. 1). The channel micromirrors 103 are positioned in accordance with the spatial array formed by the spectral channels, such that each channel micromirror receives one of the spectral channels. The channel micromirrors 103 may be individually controllable and movable, e.g., pivotable (or rotatable) under analog (or continuous) control, such that, upon reflection, the spectral channels are directed into selected ones of the output ports (e.g., ports 110-2 through 110-N) by way of the focusing lens 102 and the diffraction grating 101. In this manner, the MEMS device 103 may be used to selectively couple the spectral channels between the input and output ports of the system. The system 100 may also include a quarter-wave plate 104, which causes each spectral channel to experience a total of approximately 90-degree rotation in polarization upon traversing the quarter-wave plate 104 twice. This and other examples of optical systems employing arrays of MEMS devices (e.g., micromirrors) are described in U.S. Pat. Nos. 6,687,431; 6,661,948; 6,625,346; and 6,549,699, which are assigned to the present assignee and incorporated herein by reference.
In optical systems employing MEMS devices, such as the system shown in FIG. 1, switching individual elements within a MEMS device can cause disturbances in neighboring elements. For example, switching mirrors in a MEMS array has been found to cause an aerodynamic coupling with other mirrors in the array that can disturb mirrors that are to remain static. Efforts have been made to cancel this disturbance in non-switched or static mirrors. These efforts have focused on selecting a control strategy to minimize the perturbing effects of the mirror being switched. For example, previous work has involved designing an optimal trajectory for the switched mirror, incorporating knowledge of the system dynamics, in order to minimize disturbances. One such solution is discussed in U.S. Pat. No. 5,668,680 of Tremaine. Other efforts include slowing the motion of the switched mirror, optimizing the voltage versus time profile that creates mirror motion, and providing a mechanical blockage between mirrors.
The present invention provides a system and method for canceling disturbance in a MEMS device that controls the non-switched elements in the MEMS device in a manner that resists perturbation.